Capable ensembles of early-career actors aren't uncommon in Chicago's huge, non-Equity theater scene — increasingly the preferred theatrical destination for the well-trained and only just out of school.

These days, open-minded, risk-inclined directors have plenty of fresh choices from this demographic (assuming no one has to sing). But the young, mostly-unknown-in-town cast of Jonathan Berry's deeply affecting production of "Punk Rock" at the Griffin Theatre is, taken as a whole, remarkable enough for your mouth to keep dropping open in surprise at the depth and raw frankness of their work. It's like a trout farm of talent, swimming around in their school uniforms.

That jaw would not be falling without Berry's direction. He does here what I was hoping he would do with Griffin's disappointing recent production of the musical "Spring Awakening," only he couldn't or didn't. "Punk Rock" is a closely observed and dark, yet affectionate, play by British playwright Simon Stephens. Stephens is a former teacher himself; his compassionate and unsentimental work has proved so many times to be a fine match for Chicago theaters that he has handed Griffin Theatre the United States premiere of this play. It is about bright but tortured adolescents in a school near the northern England city of Manchester, where this play was first performed in 2009, and where, in full disclosure, I was a kid myself. They try to assert themselves, look cool, pursue each other sexually and come out on top in the crucial, life-or-death standardized exams that pockmark the British educational system.

Like "Spring Awakening," "Punk Rock" is mostly about the struggles of being a teenager with too little information. These characters are surrounded by aggressors of all stripes, and pressure from adults to succeed, yet are equipped with a limited emotional vocabulary and, most frighteningly of all, an inability to see that the hellish little petri dish in which they have been thrown is, as they say in "Avenue Q," "only for now." As I sat there at Theater Wit on Thursday night, squirming in my seat while watching these goings-on, I kept thinking about the famous Dan Savage advice for LGBT teens — "It gets better" — and thinking that it could apply to everyone and be affixed to the wall of every school.

Of course, adults interested in education invariably focus on curricula and testing, forgetting, perhaps in an act of self-preservation, that when you're actually in a high school, none of that stuff affects your life anywhere near to the extent of what goes on in hallways or, in the case of this play, in a library where the senior students can hide themselves away and flail away at each other. "Punk Rock" is not an optimistic or cheery piece and is bereft of the gauzy memories that make up "The History Boys," a play it recalls. Here, if you're a parent, you'll truly find yourself fearing for these young people. And what eventually happens to them, which I will not reveal, is sitting with me still as I write.

Berry has very carefully layered, textured and theatricalized the scenes that make up about 110 intermissionless minutes in that library; he has clearly insisted that these actors not stop working for a moment — and it's the fullness of the performances that underpins the quality of Berry's gripping production, which only stutters in the last few minutes, when tension that needs to continue is allowed to falter.

In a kind of perverse and sardonic nod to an Agatha Christie thriller, Stephens has created a cast of characters, any one of whom might blow his or her top if all the bullying or the pressure gets to be too much. There's Bennett (JJ Phillips), the aggressor of the group whose hostility seems to come from an inner secret; his girlfriend, Cissy (Jess Berry), a rather odious, clever girl; and Tonya (Leah Raidt), seemingly destined to be a plain follower, never a glamorous leader. There's Nicholas (Brandon Ruiter), whose cool seems to mask something, and William (Joey deBettencourt), a total mess and one of those teens whose loquacity never masks their childish sensibilities. Those actors are all good.

But there are two blistering performances here. One is from Leah Karpel, who plays a new girl — a new girl who likes to burn herself — and creates such a fully rounded character that you feel like you know everything about her. The other is from Ryan Heindl, who plays the supersmart kid who gets bullied and who creates a wounded soul wise beyond his years, and yet is so sad and resigned, you fear at any moment he will pop and blow this library of cruelty to hell. It is far from the cliche of the type and is a deeply powerful performance from a young actor who seems totally immersed in this world.

"Punk Rock," a beautiful piece of writing, does rely on the isolation of this library from the rest of the school for its plotting to work, an isolation mentioned several times in the exposition of the piece. That absence of adults strains credulity when the crisis really comes down, although I remember such a place in my school where teachers never came. It was not my favorite spot.